Flat-screen displays are widely used in a great variety of applications such as computers, mobile phones and television sets. A prominent segment of these displays is that of liquid crystal displays (LCDs). LCDs are based on back illuminated screens, with multiple layers of different optically active films, at least one of which being a liquid crystal layer. Light transmission from each pixel can then be controlled and modulated by changing the polarization state of the liquid crystal.
Semiconductor nanocrystals relate to a class of nanomaterials with properties that are widely tunable by controlling particle size, composition and shape. Among the most evident size dependent properties of this class of materials is the tunable fluorescence emission. The tunability is afforded by the quantum confinement effect, where reducing particle size leads to a ‘particle in a box’ behavior, resulting in a blue shift of the band gap energy and hence the light emission. For example, in this manner, the emission of CdSe nanocrystals can be tuned from 660 nm for particles of diameter of ˜6.5 nm, to 500 nm for particles of diameter of ˜2 nm. Similar behavior can be achieved for other semiconductors when prepared as nanocrystals, allowing for broad spectral coverage from the UV (using ZnSe, CdS for example) throughout the visible (using CdSe, InP for example) to the near-IR (using InAs for example). The use of semiconductor nanostructures for color tuning of the LC display have been suggested in [1].
Changing the nanocrystal shape was demonstrated for several semiconductor systems, with the most prominent shape being the rod shape. Nanorods show properties that are modified from the spherical particles. For example, the nanorods exhibit emission that is polarized along the long rod axis, while spherical particles exhibit unpolarized emission. Moreover, nanorods have advantageous properties in optical gain, suggesting their potential use as laser materials as shown for example in [2]. The emission from a single nanorod was also demonstrated to be switched on and off, reversibly, under an external electric field, as described for example in [3].
An attractive property of colloidal semiconductor nanoparticles is their chemical accessibility, permitting their processing in various diverse means. The particles may be deposited from solution, spin coated or deposited in films, embedded in plastics and more.